The purpose of the proposed research is to elucidate tho biochemistry, physiology, and structure of new coenzymes and vitamins that have been discovered in methanogenic bacteria. In the history of biochemistry, microbes have played a pivotal role in the assay of vitamins as well as in the elucidation of the biochemical function of vitamins and coenzymes. To completely understand cell chemistry is important, for biochemical deficiences produce a diseased state. So far the structures of 6 new coenzymes of methanogens have been documented. It is our goal to define the biochemistry of carbon dioxide reduction to methane, a process which requires the participation of these coenzyme. The major specific aims for this applications are; (i) to study the activation and reduction of carbon dioxide that leads to the formation of a formyl group on the coenzyme, methanofuran, a new method of carbon dioxide fixation; (ii) to study the reduction of a methylene group attached to the coenzyme, tetrahydromethanopterin, and define the products of the reaction; (iii) to define the electron carriers that are involved in these enzymatic reductive reactions; (iv) to study the reductive regeneration of the mercapto form of each of two coenzymes (HS-CoM and 7- mercaptoheptanoylthreonine phosphate) from their heterodisulfide, which is the oxidized product of the terminal methanogenic reaction; (v) to isolate and determine the structure of a vitamin required for the growth of Methanomicrobium mobile. We cannot predict whether these coenzymes will be of chemotherapeutic value in human disease, or whether they will contribute only in a general understanding of biochemistry. The discovery of the archaebacteria is only about a decade old, and since these organisms differ in many ways from typical bacterial, it is important to fully document their biochemistry and identify potential uses to benefit man.